1. Field of the Invention
The present invention relates to methods of temporarily reducing the permeability of one or more selected sections of a subterranean formation penetrated by a horizontal well bore and when required, restoring the permeability of the selected sections.
2. Description of the Prior Art
The drilling of horizontal well bores from existing well bores has improved the production capacity of the wells. In addition, the drilling of horizontal well bores from existing well bores brings about lower drilling costs, reduced capital expense and higher percent recovery of oil and gas.
In order to control the production rates from different segments of horizontal wells or from different horizontal well bores, sophisticated completion hardware has heretofore been installed such as horizontal well bore flow control apparatus, sensors, data transmission devices, wireless remote control apparatus, pressure monitoring devices and the like. While the installation of such hardware for production rate control has definite advantages in deep off-shore wells where the use of conventional techniques are very expensive, more economical means of production rate control are needed in on-shore wells and other shallow wells that include horizontal well bores. A problem that often occurs in the production of hydrocarbons from horizontal well bores in producing zones is that the portion of the subterranean formation penetrated by the heel of the horizontal well bore often experiences higher draw-down pressure than the other portions of the well bore including the toe. The term “heel” refers to the portion of the horizontal well bore where the well bore begins its curvature to horizontal and the term “toe” refers to the end portion of the horizontal well bore. As a result of the higher draw-down pressure in the heel portion, higher production rates result from the heel portion than from the other portions of the well bore when the entire horizontal well bore is produced. This leads to higher hydrocarbon production rates from the heel portion which in turn may lead to early water break-through. Consequently, the full production potential of the other portions of the horizontal well bore in the producing zone may never be realized.
Other problems that are often encountered in subterranean producing zones penetrated by horizontal well bores include the inability to control production from sections of varied permeability in the subterranean zone, the inability to eliminate cross-flows in the horizontal well bore and the inability to achieve zonal isolation in the well bore.
Thus, there are needs for improved methods utilizing chemical processes for reducing the permeabilities of selected sections of horizontal well bores or of the entire lengths of the well bores and for restoring the permeabilities when desired.